• Energy Research

The current status of FW generation, including its characteristics, management, and current challenges in China, were analyzed, and further suggestions were made with regards to improvement. About 19.50% of the FW generated could be treated under the current designs for treatment capacity in China. FW characteristics show great variability in different economic regions in China, where both treatment efficiency and FW management are poor. Combined pretreatment and three-phase separation is the most used pretreatment method, and of the current FW pilot projects, anaerobic digestion is the most prevalent, accounting for 76.1% of all projects. Significant regional characteristics have been identified regarding FW generation and the treatment capacity for FW processing. Possible factors influencing FW management in China were also discussed. Finally, detailed suggestions are given for further development of FW treatment capacity, particularly regarding potential technical routes and management measures.

The effects of thermal pretreatment at moderate temperatures (70, 80 and 90 °C) and high temperatures (120, 140 and 160 °C) over heating durations of 10-120 min on the physical and chemical properties of kitchen waste and on anaerobic digestion were investigated. The results show that thermal pretreatment significantly enhances the solubilisation of organic compounds (chemical oxygen demand, crude proteins, crude fats and volatile fatty acids) and their biodegradability during subsequent anaerobic digestion. High temperature and long heating duration are beneficial for the release and reduction of organic compounds, and the efficiency of subsequent anaerobic digestion is improved markedly under these conditions. Moreover, both the methane production rate and methane yield were observed to increase significantly at moderate treatment temperatures when the anaerobic digestion time was longer than 50 h.

The effect of thermal pretreatment (55–160 °C) on the degradation characteristics of kitchen waste during anaerobic fermentation at medium temperature was investigated. The breakdown of both organics and inorganics and the enhancement of biogas production in batch tests caused by thermal pretreatment during subsequent anaerobic fermentation were examined. Considering the effect of the acidification products and ammonia nitrogen in the acidification phase on subsequent biogas production, the influencing factors and related characteristics of various fermentation types were investigated. The results indicate that thermal pretreatment cannot only promote the anaerobic degradability of KW and the biogas production from KW but can also reduce the retention time necessary for anaerobic acidification by five days. At 50–70 °C and 140–160 °C, the biogas production and organic removal rates of the subsequent anaerobic digestion process decreased slightly, whereas at 90 and 120 °C, superior results were achieved during digestion.

Abstract Our society currently faces the twin challenges of resource reclamation from rapidly escalating KW (kitchen waste) and increasingly expensive depletion costs and restrictive disposal legislation due to environmental impacts and fast depleting global resources necessitate action. This work studied the influence of thermal hydrolysis on the utilization of KW based on the principle of split phase processing, including solid phase for pig feed, liquid phase for anaerobic digestion and floating oil for biodiesel. It shows that the solid phase of KW after thermal treatment could satisfy the nutrition content requirements as raw materials for pig feed. The efficiency of the subsequent anaerobic digestion of liquid phase increased for KW pretreated at 120 °C and higher methane production and soluble chemical oxygen demand reduction were achieved after a pretreatment time of 40 min. Composition analysis of floating oil during thermal hydrolysis indicates that unsaturated fatty acid accounts for more than 61% and the main ingredients are monounsaturated fatty acid (more than 36%). All parameters important for biodiesel quality except the acid value could satisfy the biodiesel requirements according to the European standard. From overall analysis, the thermal pre-treatment was profitable with output value of $ 57.52 ton−1 KW.

The effects of thermal pretreatment (90, 120, 140 and 160 °C) on the morphology (organic and inorganic nitrogen) and distribution properties (in solid phase, liquid phase and gas phase) of nitrogen in kitchen waste (KW) and on anaerobic digestion performance were investigated. The results show that thermal pretreatment could efficiently enhance the solubilisation of organic nitrogen compounds in KW, especially at high temperatures and long heating durations. Approximately 3.0–47.9% of organic nitrogen in KW decreases in total nitrogen content was obtained in the solid phase after thermal pretreatment. Higher biogas production and biodegradability of organics (in terms of the removal rate of soluble chemical oxygen demand, total organic nitrogen, and volatile solids) during subsequent anaerobic digestion were observed compared with the levels for untreated KW. An overall economic analysis indicates that the most profitable pretreatment process was achieved at 90 and 120 °C for treatment time of 30 and 15 min respectively, with a net potential profit (2–8 € ton−1 kW).

Abstract In this study, batch tests were performed to evaluate the effects of different thermal pretreatment temperatures (55–160 °C) and durations (15–120 min) on the anaerobic digestion of kitchen waste (KW). Two commonly used approaches, namely the modified Gompertz model and the approach developed by Koch and Drewes, were applied to assess the effects of the different pretreatment parameters on the biomethane yield, lag time and hydrolysis rate constant via data fitting. The subsequent anaerobic digestion of KW pretreated at 55–120 °C presented greater efficiency, and longer treatment durations resulted in increased methane production and higher hydrolysis rate constants. These findings were obtained due to the lower nutrient loss observed in KW treated at lower temperature treatments compared with that found with higher temperature treatments. In general, the effects of thermal pretreatment on the lag phase and hydrolysis rate differed depending on the treatment parameters leading to the variations in the KW compositions. The soundness of the two model results was evaluated, and higher statistical indicators (R2) were found with the modified Gompertz model than with the approach developed by Koch and Drewes.

Abstract The influence of thermal hydrolysis (i.e., 90 °C, 120 °C and 140 °C) under heating durations ranging from 20 to 60 min on an organic solution and the FA (fatty acid) composition of waste cooking oil in KW (kitchen waste) were investigated. The influence of the FA composition on biodiesel quality was also studied. The results indicate that higher treatment temperature and longer treatment duration of thermal hydrolysis could significantly increase soluble chemical oxygen demand and floating oil content of KW. Composition analysis of FA during thermal hydrolysis indicates that UFA (unsaturated fatty acids) accounts for more than 62%, and the main ingredients are MUFA (monounsaturated fatty acids), which primarily existed in n-6 UFA and n-9 UFA. Linoleic acid constitutes 90% of PUFA (polyunsaturated fatty acids), and the chief components of UFA (n-3, n-6, n-7 and n-9) are α-linolenic acid, linoleic acid, vaccenic acid and oleic acid, respectively. In addition, palmitic acid and stearic acid constitute more than 95% of SFA, and the ratios of PUFA/SFA, MUFA/SFA and n-6/n-−3 PUFA increased during the thermal hydrolysis process. All parameters important for biodiesel quality except the oxidation stability could satisfy the biodiesel requirements according to the European standard.